1. Field
Embodiments of the present invention generally relate to apparatus, systems, and methods for forming plasma and, more specifically, to apparatus, systems, and methods for generating and distributing RF waves within a plasma reactor.
2. Description of Related Art
RF plasma reactors are commonly used in the production of microelectronic circuits. Plasma reactors generally form and maintain a plasma within a process chamber from a process gas or process gas mixture supplied to the chamber. The RF source power utilized to form the plasma typically may be coupled either inductively or capacitively into the chamber. In cases in which capacitive coupling is used to apply RF source power, for example, an RF source power generator may be coupled to an overhead electrode (facing a substrate disposed on a substrate support) to supply sufficient RF power at a frequency selected to cause the plasma to be formed. In order to maintain a plasma in the chamber, the overhead electrode continues to transmit RF power into the plasma via the overhead electrode. However, conventional RF plasma reactors often develop a non-uniform spatial distribution of the RF power (e.g., the laterally or radially arranged profile showing where the RF power peaks and valleys fall) within the plasma
One problem that can arise in such reactors is due to the unacceptably high degree of variation in the RF power distribution within the plasma and/or with respect to the top surface of the substrate being processed is an unacceptable variation in characteristics in the substrate being processed within the reactor. For example, in an etch process, non-uniformities in the etch rate, critical dimension (CD), sidewall profiles, or other feature characteristics may be undesirably high. In deposition processes, the film thickness, composition, and other characteristics may also be undesirably non-uniform. To the extent features being formed on substrates become finer and more intricate, such non-uniformities may increase, in prevalence, severity, or both. By contrast, greater control of and/or more even distribution of RF power within the plasma and/or with respect to the top surface of the substrate being processed may advantageously improve processing results, thereby contributing to process robustness and predictability. Thus, plasma generation and maintenance processes, apparatus and systems associated with good control over RF power distribution are highly desirable.
Thus, there is a need for improved plasma generation and maintenance processes, apparatus, and systems.